Many high resolution digital images exhibit chromatic aberration (CA), where the color channels appear shifted. This is primarily due to the fact that as the sensor resolution of digital cameras has steadily increased over the past few years, it has not been accompanied by an increase in the quality of the optics. Unfortunately, merely compensating for these shifts is often inadequate, because the intensities are modified by other effects such as spatially-varying defocus and in-camera sharpening.
Techniques have been proposed to reduce the effects of CA. Classical techniques rely on optimal lens design or special hardware to recover the aberration coefficients through wavefront measurements (e.g., using a diffraction grating and scanning electron microscope or some form of interferometer). Others rely on primarily software solutions. One such technique involves precalibrating the color channels for optimal focus, magnification, and shift. However, producing a CA-free image subsequently requires taking three separate images, each using the optimal settings for a different color channel. Another technique uses only a single image by warping the red and green color channels to the blue channel. This is accomplished by filting edge displacements with cubic splines, with blue edges as the reference. However, they do not account for the attendant relative defocus and intensity distortion (e.g., under- and over-shooting) effects. In addition, because the displacement maps computed as part of this technique do not explicitly model the image formation process, it is not clear if the extracted maps can be used to correct a different image taken by the same camera. This is because the extracted maps are highly dependent on the relative density and distribution of the edges, which are typically unique to each image.